The Filoviruses Ebola and Marburg are highly pathogenic and contagious viruses making them a potential bioweapon. The lethal nature of these agents has made them difficult to study because of the requirement for biosafety level 4 containment. However, individual components of these virions can be safely studied in isolation. Envelope function can be studied in the context of pseudotypes and virus-like particles can be generated by the expression of the matrix protein. Recently, we have developed methods that allow the visualization of HIV using fluorescent deconvolution microscopy. With these tools it is possible to directly observe virus binding and entry into target cells in real time. These direct observations of particle behavior have provided important new insights into how HIV interacts with target cells. The goal of this application is to adapt these methods to study filovirus entry. Envelope function will be studied in two contexts. First, fluorescently labeled HIV will be pseudotyped with filovirus envelope. These studies should provide new insights into the entry pathway for Ebola and Marburg. Secondly, we will develop a system using a green fluorescent protein (GFP) tagged matrix protein (VP40) to visualize VLPs that contain the filovirus envelope. The VLP system will require extensive development and validation but offers the opportunity to study the interaction of replication defective filovirus particles with target cells. Direct visualization of these viruses will provide important new insights into how these agents bind to and enter target cells. [unreadable] [unreadable]